JPH06297833A - Recording paper for ink-jet - Google Patents

Abstract

PURPOSE:To prevent density irregularity from being generated, by a method wherein in a matter comprised by providing a coated layer comprised of a coating containing white pigment on at least one surface of base paper, a matter whose stocking sizing degree, apparent density and a formation index value are specific is used as the base paper CONSTITUTION:In recording paper which is used for ink-jet recording to which aqueous ink is used, at least one surface of base paper is provided with a coated layer coated with a dried quantity of coating at 4-10g/m<2> containing a white pigment. In this case, the base paper wherein a degree of fine personal size is 5-70 seconds, apparent density is 0.70-1.00g/cm<2> and a formation index value is at least 20 is used. With this construction, even is a thickness of the coated layer is made thin in a solid printing part, generation of density irregularity at a half tone printing part can be prevented almost and recording paper for ink-jet superior in color development clarity or resolving properties can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording paper suitable for ink jet recording using a water-based ink, and more particularly to an ink jet recording paper in which uneven density hardly occurs in a solid printing portion and a halftone printing portion.

[0002]

2. Description of the Related Art As an ink jet recording paper used for ink jet recording using an aqueous ink, for example, one having a structure in which a coating layer for receiving ink is provided on a base paper is known. In this type of inkjet recording paper, the strength of the coating layer is strong, there is no powder drop that the coating layer peels from the base paper, and the coating layer is formed in order to make it like plain paper at low cost. The coating amount of the coating material is reduced or the coating material of the coating layer is mixed between the fibers of the base paper to make the thickness of the coating layer relatively thin.

However, the conventional ink jet recording paper having a thin coating layer cannot absorb the ink only with the coating layer, and as a result, the ink permeability is easily influenced by the base paper. Therefore, if the base paper has unevenness of ink permeability, especially solid print areas and halftones
There is a problem that density unevenness, which makes the density uneven in the printing portion, tends to occur.

The following have been proposed as technical means for eliminating such density unevenness. For example, in JP-A-61-68286, the basis weight is 50 to
A recording paper having a coating layer on a base material having a 90 g / m ² and a Steckigt sizing degree of 5 to 100 seconds is used, and a water content is 10 to 90% by weight in order to enhance ink absorbability.
An ink jet recording method for performing printing using the water-based ink of JP-A-6-68287 is disclosed in JP-A-6-68287.
A recording paper similar to that of the recording method of 1-68286 is used, and the viscosity is 25 cp in order to enhance ink absorbability.
An ink jet recording method for performing printing using the following inks is disclosed in JP-A-61-268288.
A recording paper similar to the recording method of Japanese Patent Laid-Open No. 1-68286 is used, and the surface tension is close to that of the recording paper in order to specify the spread of the dots, 20 to 60 dyn / cm (20 ° C.).
Inkjet recording methods for performing printing using the above ink have been proposed. In addition, JP-A-62-2
Japanese Patent No. 16785 discloses a recording having a structure of only base paper (without a coating layer) in which the peak wavelength in the power spectrum of the surface shape of the recording surface is specified in order to improve the ink absorption and improve the dot shape. Paper is proposed.
Further, in JP-A-1-159287, a base paper having a Steckigt sizing degree of 1 to 8 seconds and an ash content of 2 to 15% is used, and it has appropriate hydrophobicity as a binder of a coating layer. Recording papers that use paper have been proposed.

[0005]

However, the techniques disclosed in JP-A-61-68286, JP-A-61-68287 and JP-A-61-68288 are all disclosed.
It is characterized in that a specific recording paper and ink are used in combination, and therefore, the above-mentioned unevenness in density cannot be significantly improved only by the recording paper in which the basis weight and the Steckigt sizing degree of the base paper are specified. Also, JP-A-62-216
Since the recording paper of Japanese Patent No. 785 does not have a coating layer, it has poor ink absorbency and lacks the color developability and resolution of the printing portion, and the ink is directly absorbed by the base paper. Therefore, the phenomenon of ink permeation along the fibers occurs, and the dot shape deteriorates. Therefore, it is difficult to sufficiently improve the density unevenness. Furthermore, JP-A-1-15928
Also in the recording paper of JP-A-7, there is a variation in ink permeability, and it is also difficult to sufficiently improve the density unevenness.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to obtain density unevenness in a solid printing portion or a halftone printing portion even if the coating layer is thin. An object of the present invention is to provide an inkjet recording paper that hardly occurs, is excellent in color vividness and resolution, and has a strong coating layer strength.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies in order to solve the above-mentioned problems, and as a result of studying the problem of density unevenness in particular, as a result, it has been found that Occurrence occurs when the dry coating amount is 4 to 10
In an inkjet recording paper having a thin (light-weight) coating layer of g / m ^2, it was clarified that it was caused by three factors of the texture index value of the base paper, the Steckigt sizing degree and the apparent density.

That is, first, as described above, in recording paper having a thin coating layer, the ink cannot be completely absorbed by the coating layer, and therefore the ink which cannot be completely absorbed must be absorbed by the base paper. Therefore, if the texture of the base paper on the recording paper is poor, that is, if there is a minute difference (variation) in the basis weight distribution, a difference occurs in the size of the voids between the base paper fibers,
I was able to know that uneven density occurred.

That is, in the portion where the gap between the base paper fibers is large and the ink is easily absorbed, the penetration depth of the ink is deep and the dot diameter is reduced, while in the portion where the void is small and it is difficult to absorb the ink, the ink is laterally spread. It was confirmed that the dot diameter increased due to the expansion in the direction, and as a result, the dot diameter varied between the two and uneven density occurred. In addition, when the texture of the base paper is poor, when coating the paint that forms the coating layer, the gap between the fibers of the base paper is small. It is easily absorbed and the coating layer becomes thin. On the contrary, the coating layer becomes thicker in a portion having a large void and a high basis weight. And, in the thin portion of the coating layer, the dot diameter is large because the ink absorption amount of the coating layer is small, while in the portion where the coating layer is thick, the dot diameter is small because the ink absorption amount of the coating layer is large. As described above, it was confirmed that even if the thickness of the coating layer was uneven, the dot diameter was varied and the density was uneven.

When the Steckigt sizing degree of the base paper is less than 5 seconds, unevenness in the effect of the sizing agent on the base paper occurs, resulting in uneven density. When the value exceeds 5 seconds, the unevenness of effect of the sizing agent occurs. It was found that the density unevenness did not occur because it disappeared.

In other words, if the effect of the sizing agent on the base paper is uneven, the penetration of the ink into the base paper is slow at the portion where the sizing agent works well, so that the ink overflows in the coating layer and the dot diameter increases. On the other hand, in the portion where the effect of the sizing agent is poor, the penetration of the ink into the base paper is good, and the dot diameter becomes small. Therefore, it was confirmed that the dot diameters varied and uneven density occurred. Further, in a portion where the sizing agent works well on the base paper, the coating material forming the coating layer hardly penetrates into the inside of the base paper, so that it easily remains on the upper portion of the base paper, and the coating layer is formed thick. In areas where the sizing agent is not effective, the coating layer becomes thin because the coating material easily penetrates into the base paper. It was confirmed that the unevenness in the thickness of the coating layer causes the dot diameter to vary and the uneven density to occur for the same reason as described above.

Further, it has been found that the apparent density of the base paper also affects the density unevenness. In other words, if the apparent density is low, the internal voids of the base paper will be large, so the paint will easily penetrate into the base paper, and the coating layer will be thin. Conversely, if the apparent density is high, the paint will be difficult to penetrate, and the coating layer will be Get thicker. Therefore, it was confirmed that the dot diameters varied and the density unevenness occurred for the same reason as described above.

As a result of further research based on such findings, the present inventors have found that it is possible to minimize the variation in ink permeability of the base paper and to form a coating layer having a uniform thickness. By improving the texture of the base paper (reducing the basis weight distribution of minute parts) and specifying the Steckigt sizing degree and apparent density, density unevenness especially occurs even on inkjet recording paper with a thin coating layer. The inventors have found that the above can be prevented and have completed the present invention.

That is, the ink jet recording paper of the present invention comprises an ink jet recording paper having a coating layer containing a coating material containing a white pigment at a dry coating amount of 4 to 10 g / m ^{2 on} at least one side of a base paper. In the recording paper for use as the above-mentioned base paper, the Steckigt sizing degree is 5 to 70 seconds, the apparent density is 0.70 to 1.00 g / cm ^3, and the texture index value is 20.
It is characterized by using the above-mentioned base paper.

In the above technical means, the Steckigt sizing degree of the base paper is measured according to JIS P 8122 and is 5 to 70 seconds, preferably 10 to 60 seconds. If the Stekihist size degree is less than 5 seconds, unevenness in the effect of the sizing agent is likely to occur, and density unevenness is likely to occur. On the contrary, if it exceeds 70 seconds, the effect of the sizing agent becomes strong as a whole. Since the wettability of the coating material for forming the ink on the base paper is deteriorated, the coating material is easily repelled, and unevenness in the thickness of the coating layer occurs, resulting in uneven density.

The apparent density of the base paper is 0.70 to 1.
00 g / cm ³ , preferably 0.75 to 0.90 g / c
m is ^3. If the apparent density is less than 0.70 g / cm ³ , the coating easily penetrates into the base paper, the coating layer becomes thin and density unevenness is likely to occur, and the binder component in the coating is added to the base paper. It penetrates and the coating strength of the coating layer decreases. On the other hand, if it is more than 1.00 g / cm ³ , the absorption speed of the ink is remarkably reduced, and color mixture bleeding occurs.

Further, the texture index value of the base paper is 20 or more, preferably 25 or more. When the texture index is less than 20, the density unevenness becomes remarkable as described above.

This texture index value is M / K System
ms, Inc. A 3D sheet analyzer (M / K950) manufactured by (MKS Co.) was used, and the diameter of the analyzer was set to 1.5 mm, and the measurement was performed using a micro formation tester (MFT). That is,
A sample is mounted on a rotating drum in a 3D sheet analyzer, and a light source mounted on the drum shaft and a photodetector mounted on the outside of the drum corresponding to the light source are used to determine the difference in the local basis weight of the sample. To measure. The measurement target range at this time is set by the diameter of the diaphragm attached to the light entrance part of the photodetector. Then, the light amount difference (deviation) is amplified and A / D converted, classified into 64 light measurement basis weight classes, 100,000 data are taken in one scan, and the histogram frequency for that data is taken. To get Then, the highest frequency (peak value) of the histogram is divided by the number of classes having a frequency of 100 or more out of those classified into the classes corresponding to 64 minute basis weights, and the value obtained by dividing it by 1/100 It is calculated as an index value. The larger the texture index value, the better the texture.

As a method for improving the texture of the base paper, for example, a screen or a vortex cleaner is installed immediately before the head box of the paper machine so that the flow direction of the base paper material is not constant, or Examples include, but are not limited to, a method of controlling floc formation of the raw material using an additive chemical such as a dispersant, a texture control additive, a retention agent and a drainage aid.

Further, in the above technical means, as the base paper, one which is usually formed from wood pulp as a main raw material is used, and if necessary, a mixture of glass fiber and synthetic fiber is used. Good. A filler is compounded in this base paper, and as the filler, white fillers such as heavy or light calcium carbonate, talc, kaolin clay, titanium dioxide, zeolite, and white carbon can be used.
This filler is added in an amount of 5 to 3 to improve the opacity of the base paper.
It is blended in a proportion of 0% by weight, preferably 10 to 25% by weight. If this filler is blended in excess of 30% by weight,
The strength of the base paper and the generation of paper dust become remarkable.

This base paper has a basis weight of 50 to 100 g /
m ^2, preferably 60 to 90 g / m ^2, and the addition paper thickness 65～150Myuemu, is papermaking to preferably be 80～140Myuemu. If the basis weight is less than 50 g / m ² , back slipping tends to occur, while if it exceeds 100 g / m ² , the strength of the paper becomes large and the buckling force increases, leading to conveyance troubles in the recording apparatus. It will be easier. Similarly, if the thickness of the paper is less than 65 μm, back-swing or the like occurs, and if it exceeds 150 μm, the strength of the paper increases and the buckling force increases, which easily causes conveyance rubbing in the recording apparatus. Become.

The BET specific surface area is 10 as a coating layer-forming coating material to be coated on at least one surface of such a base paper.
0 to 400 m ² / g, preferably 200 to 400 m ² / g
It is desirable to use a coating material containing a white pigment having an average particle diameter of 2 to 15 μm. As such white pigment, for example, amorphous silica is most suitable. The white pigment is added to the coating material in an amount of 50 to 85% by weight, preferably 60 to 80% by weight.

The white pigment has a BET specific surface area of 100 m ² /
When it is less than g, the ink absorption capacity of the coating layer is lowered, so that color mixture bleeding is likely to occur, and conversely 400 m ² /
When it exceeds g, the hardness of the pigment decreases and the pigment becomes extremely soft, so that writing with a pencil or the like becomes difficult. If the average particle diameter of the pigment is less than 2 μm, it is difficult to write with a pencil or the like, and if it exceeds 15 μm, the unevenness of the surface of the coating layer becomes large, so that the ink flows out in a certain lateral direction around the concave portion, As a result, the dot shape at the time of recording becomes non-uniform, and density unevenness and color mixture bleeding easily occur.
Further, when the amount of the white pigment compounded is less than 50%, the same adverse effect as when the BET specific surface area of the pigment is less than 100 m ² / g is exerted, and when it exceeds 85% by weight, the strength of the coating layer decreases. However, powder fall-off easily occurs, and writing with a pencil or the like becomes difficult.

The white pigment of amorphous silica may be modified with a cationic metal ion such as Ca, Al or Mg in order to impart water resistance and light resistance.
Further, depending on the purpose, the BET specific surface area is 100 m ² / g
You may mix a small amount of the pigment below.

As the binder component in the paint, polyvinyl alcohol derivatives such as completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol and silanol group-modified vinyl alcohol copolymer, cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose and hydroxypropyl methyl cellulose, polyvinyl pyrrolidone. , Water-soluble polymers such as oxidized starch, modified starch, gelatin, casein, and acrylic acid polymers are used alone or in combination. Among them, polyvinyl alcohol-based polymers such as completely saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and silanol group-modified vinyl alcohol copolymer are preferable from the viewpoint of the strength of the coating layer, and further, silanol group-modified vinyl alcohol copolymer. Is most preferable because it can further improve the strength of the coating layer and can increase the blending amount of the pigment for capturing the dye in the ink.

In addition, for the purpose of imparting water resistance of the image of the water-based ink to the coating layer, an amine-based polymer such as polyethyleneimine and polyacrylamine salt, or the like, in the coating,
In addition to the primary salt, a cationic aqueous polymer composed of a copolymer of an acrylic compound and an ammonium salt, or a water-soluble metal salt may be blended alone or in combination of two or more.
Further, the coating material may optionally contain a fluorescent whitening agent, a surfactant, an antifungal agent, a dispersant, and the like.

The recording paper of the present invention has a dry coating amount of 4 to 10 g / in at least one surface of the above-mentioned base paper.
The coating is performed so that the coating amount is m ² , preferably 4 to 8 g / m ² .
If the coating amount is less than 4 g / m ² , the fibers of the base paper will be mixed in the coating layer, and the ink permeability will vary, resulting in non-uniform dot diameters and uneven density. At the same time as the occurrence, the color developability and resolution deteriorate. On the contrary 10
If it exceeds g / m ² , the strength of the coating layer itself is deteriorated, which may cause powder falling. As a coating means, a reverse coater, an air knife coater, a blade coater, a gate roll coater, or the like can be appropriately adopted.

Further, in the present invention, the surface of the recording paper is supercalendered if necessary so that the dots printed on the recording paper are close to a perfect circle and the peripheral edge thereof has a shape with little roughness. The Beck's smoothness is finished at 25 seconds or more, preferably 25 to 100 seconds by the above treatment.

[0029]

In the recording paper of the above-mentioned technical means, the base paper has a uniform void distribution and the coating layer formed on the base paper has a uniform thickness. Has uniform permeability over the entire area of the recording paper (even in units of minute areas), and density unevenness does not occur even when solid and halftone recording is performed by inkjet recording with a conventionally known aqueous ink. Moreover, the recorded image is excellent in color vividness and resolution.
The strength of the coating layer is also sufficient. This recording paper can be used in an ink jet recording method using a conventionally known water-based ink, and the water-based ink used in the recording method is not particularly limited.

[0030]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

Examples 1 to 8 and Comparative Examples 1 to 8 Hardwood bleached kraft pulp was used as the raw material pulp, and the basis weight was 80 g / m ² (however, in Example 4 and Comparative Example 7, 70).
g / m ² , Example 5 is 100 g / m ² , Comparative Example 4 is 60 g
/ M ² ) so that the apparent density, the Steckigt sizing degree, and the formation index value become the values shown in Table 1, and the respective base papers were prepared.

Next, on one side of each of these base papers, the following composition components, fine particle synthetic amorphous silica (BET specific surface area 300 m ² /
g, manufactured by Mizusawa Chemical Co., Mizukasil P-78D): 72% by weight Polyvinyl alcohol (manufactured by Kuraray, PVA117): 2
3% by weight of waterproofing agent (Nippon Shokubai Kogyo, Epomin P1000): 5
A coating material as a coating agent containing 10% by weight was applied in a dry coating amount shown in Table 1 to form a coating layer. Then, the coated surface was finished so that the Bekk smoothness was 30 seconds, and recording papers of Examples and Comparative Examples were obtained.

[0033]

[Table 1]

Using these recording papers, a printer having an ink jet recording head of four colors of black, cyan, magenta and yellow and having a recording density of 300 dpi, a viscosity of 1 to 8 cp and a surface tension of 40 dyn / An image was recorded using a water-based ink having a size of not more than 10 cm, and the density unevenness of the image, the color vividness, the resolution, and the strength of the coating layer on each recording paper were examined and evaluated. Each evaluation was performed according to the method described below.

The density unevenness was evaluated by visually observing the obtained image after printing a 50% halftone pattern with a cyan color ink and observing the following criteria. ⊚: No density unevenness occurs, ◯: Very slight density unevenness occurs, Δ: Small density unevenness occurs, ×: Density unevenness occurs.

The color vividness was evaluated by visually observing the color vividness of the obtained color image after printing a color image with the above printer and evaluating the superiority and inferiority thereof according to the following criteria. ⊚: Very good, ◯: Good, Δ: Normal, ×: Bad.

The resolution is 8 points for Mincho type and is "dark",
The character "Wealth" was recorded, the intelligibility and character quality were visually judged, and the superiority or inferiority was evaluated according to the following criteria. ⊚: Both the intelligibility and the quality of the characters are very good, ◯: Both the intelligibility and the quality of the characters are good, Δ: The characters are slightly broken, ×: The characters are broken.

The strength of the coating layer was determined by bending the recording paper, rolling a 2 kg metal roll on the bent portion, observing the state of peeling of the coating layer at this time, and evaluating the superiority or inferiority thereof according to the following criteria. . ⊚: Not peeled at all, ◯: Peeled slightly, Δ: Peeled slightly, ×: Peeled considerably.

Table 2 also shows the results of the above evaluations.

[0040]

[Table 2]

[0041]

As described above, according to the present invention,
Even if the thickness of the coating layer is thin, there is no density unevenness in the solid print part and the halftone print part, and it is possible to record an image by the inkjet recording method using a water-based ink that is excellent in color vividness and resolution Become. Further, the coating layer is sufficiently excellent in strength and does not cause powder drop. Furthermore, the recording paper of the present invention is low in cost because the coating amount of the coating material for forming the coating layer is very small, and the feel and appearance of the recording paper are similar to those of plain paper.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location D21H 21/14 7199-3B D21H 5/00 Z

Claims (1)

[Claims] 1. An inkjet recording paper comprising a base paper and a coating layer coated with a coating material containing a white pigment at a dry coating amount of 4 to 10 g / m ² on at least one side of the base paper. An inkjet recording paper comprising a base paper having a Steckigt sizing degree of 5 to 70 seconds, an apparent density of 0.70 to 1.00 g / cm ³ and a texture index value of 20 or more.